The present invention relates to an improved valve which is a self-contained emergency shutdown valve which is manually and spring operated and which will close any time its high or low pressure presettings are exceeded.
Prior to the present invention, there have been emergency shutdown valves, which valve is either hydraulically or electrically operated. This requires that the source of power (hydraulic or electric) be available at the valve to ensure that the valve will close responsive to line conditions. The unit manufactured by Barber Industries Ltd. of Calgary, Alberta Canada (T2H 2P3) and Edmonton, Alberta, Canada (T6E 4S8) and having the name of RA-PRESCO-DYNE, which device is designated to be a self-contained emergency shutdown system for reverse acting gate valves which are actuated either electrically or hydraulically.
U.S. Pat. No. 3,429,321 discloses a safety valve actuator which uses springs for high and low set points, uses a spring to close the valve and manually resets the valve after tripping. A pivoted trigger is positioned to engage a shoulder on the stem to prevent its closing movement until the trigger is pivoted out of engagement with the shoulder. Pivoting of the trigger is the result of the high-pressure trip pulling upward on one portion of the trigger and low-pressure trip pushed downward on a second portion of the trigger. Both cause the trigger to pivot and disengage from the shoulder so that the valve closes responsive to the force of the stem spring. When resetting, the valve must be held open manually until line pressure is between the high and low set points. Additionally, the low set point is adjusted by threading within the high set point adjustment. Thus any adjustment of the high set point changes the low set point.
U.S. Pat. No. 3,198,207 discloses a fluid pressure controlled shut-off valve which operates responsive to predetermined line pressures. The device is powered by the downstream pressure and is not suggestive of the structure of the improved device of the present invention.
U.S. Pat. No. 5,046,376 discloses a shaft locking or manual operating apparatus for operating a gate valve manually which includes a nut, a screw shaft and balls in the grooves of the nut and shaft to provide a limited friction device together with a wrapped spring preventing rotation in one direction except when released and the rotation of one of the nut or shaft causes axial movement of the shaft which is used to operate a gate valve or to be used to lock a shaft such as a blowout preventer ram tail rod against axial movement.
Other systems have been used for emergency shutdown of valves, but those required a source of fluid pressure.
A pilot by-pass valve has been offered to the oil and gas industry by Cameron Iron Works, Inc. in which a low pressure actuated automatic safety valve can be opened when the auxiliary pilot has shut off the supply pressure. Manual operation of the by-pass valve directs supply pressure to the valve operator. As soon as line pressure returns the auxiliary pilot to normal position, the by-pass valve cuts out and the automatic safety valve is again on automatic operation.